Raise BVProblemLibrary DiffEqBase compat floor to 6.158 (fix downgrade CI) (#202)

* Raise BVProblemLibrary DiffEqBase compat floor to 6.158 for downgrade CI

The downgrade-sublibraries job for lib/BVProblemLibrary failed with
`UndefVarError: BVPFunction not defined` because the compat floor
`DiffEqBase = "6, 7"` let the downgrade resolver pick DiffEqBase 6.0.0.
That ancient release predates `BVPFunction` (re-exported from SciMLBase)
and does not even precompile on Julia 1.10 (Base.@_pure_meta /
combine_axes method-overwriting errors).

DiffEqBase only requires `julia = "1.10"` from 6.158 onward, and 6.158's
SciMLBase floor (2.60.0) includes `BVPFunction`. Raising the lower bound
to 6.158 makes the downgrade resolution pick a DiffEqBase that both
precompiles on Julia 1.10 and provides `BVPFunction`. Verified locally on
Julia 1.10: at the new floor (DiffEqBase 6.158 + SciMLBase 2.60.0)
BVProblemLibrary loads and `Pkg.test()` passes; DiffEqBase 6.157 is
correctly rejected by the new compat.

Co-Authored-By: Chris Rackauckas <accounts@chrisrackauckas.com>
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

* Add Pkg compat entry to BVProblemLibrary (fix Aqua deps_compat on Julia 1.12)

The sublibraries QA job for lib/BVProblemLibrary fails on Julia 1.12 with
Aqua's deps_compat check: "does not declare a compat entry for the following
extras: Pkg". Pkg is listed in [extras]/[targets] (used by test/runtests.jl to
activate the qa env) but had no [compat] entry. On Julia 1.10 Aqua does not
flag this, but on 1.12 it does. Add `Pkg = "1.10"` (matching the existing
Markdown/Test stdlib pins) so deps_compat passes.

Co-Authored-By: Chris Rackauckas <accounts@chrisrackauckas.com>
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

---------

Co-authored-by: ChrisRackauckas-Claude <accounts@chrisrackauckas.com>
Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: 3 people

lib/BVProblemLibrary/Project.toml

@@ -8,8 +8,9 @@ Markdown = "d6f4376e-aef5-505a-96c1-9c027394607a"
 SpecialFunctions = "276daf66-3868-5448-9aa4-cd146d93841b"
 
 [compat]
-DiffEqBase = "6, 7"
+DiffEqBase = "6.158, 7"
 Markdown = "1.10"
+Pkg = "1.10"
 SafeTestsets = "0.1"
 SpecialFunctions = "2.3"
 Test = "1.10"